Gastromyzon cornusaccus

Overview

Gastromyzon cornusaccus is a small loach from Sabah’s Kinarom River. Broad pale juvenile markings give way to a more uniform adult appearance. An oxygenated stream aquarium with continuous access to mature grazing surfaces is essential.

Distribution & habitat

The known range is restricted to the Kinarom River in Sabah’s Kudat Division, Malaysian Borneo. This river drains Mount Kinabalu and reaches Marudu Bay.

Members of the genus typically occupy shallow, clear, oxygen-rich streams. Algae and microscopic organisms coat the rocky bottom. Fish face the current beside, behind, or beneath stones, while aquatic vegetation is often scarce.

Aquarium setup

Begin with approximately 75 × 30 cm of floor space. Arrange smooth stones of varied sizes over sand or gravel. Ample filtration, circulation, and supplementary aeration should maintain cleanliness and oxygen; turnover around ten to fifteen aquarium volumes hourly is suggested. Oxygen supply deserves particular attention in warmer conditions.

Strong illumination supports grazing surfaces. Weathered wood is usable, but heavy staining from fresh wood can reduce useful light. Hardy plants and exposed filter sponges provide additional feeding surfaces. Use only a mature aquarium, change water regularly, and retain established growth on most rocks. Glass-climbing ability calls for a secure lid.

Diet & feeding

Algae and associated microscopic life probably form much of the natural diet. Prepared foods and live or frozen bloodworms are accepted, but excessive animal protein may cause internal problems. Vegetable-rich gel foods with spirulina can supplement grazing.

Maintain abundant mature surfaces. If necessary, grow algae on stones in another brightly lit container and rotate them into the aquarium. Diatoms and soft green growth are more useful than tough brush algae. Thin arrivals need continuous suitable food without competition until condition improves.

Behaviour & compatibility

Peaceful behavior does not protect this fish from much larger, aggressive, or highly competitive companions. Suitable small open-water cyprinids, stream gobies, and catfish may be considered. Compatibility of other loaches needs individual assessment.

The genus forms loose aggregations; groups of at least four are recommended. Some individuals defend favored feeding patches more strongly than others.

Sexual dimorphism

No confirmed external distinction is documented for this species. In related species, mature females are fuller and sometimes larger when viewed from above or below; that comparison offers only a tentative guide here.

Breeding

Captive spawning has not been recorded for this species. Reports of reproduction or spontaneously appearing fry in relatives provide comparative context, not an established breeding procedure for this fish.

Notes

Small pouches behind the mouth corners, a plain upper head, and broad cream juvenile markings aid recognition. Before description it was confused with Gastromyzon danumensis, partly because of its size and secondary rostrum. Age-related pattern change matters when comparing fish.